The objective of the X-ray crystallographic investigations described in this proposal is to provide structural information required for the elucidation of the mechanisms of electron transfer and potential regulation among proteins of phosphorylating electron transport chains. Since the results of recent structural and biochemical studies indicate that electron transport chains of procaryotic organisms are prototypical of corresponding systems in higher organisms, the proposed work will focus upon proteins of bacterial origin. These proteins have the operational advantage that they are relatively easily isolated and crystallized in quantities sufficient for X-ray structure determination. The following proteins have been crystallized thus far for this work: Chlorobium cytochrome c-555, cytochrome c' (R. rubrum, Rps. palustris, A. iwasaki), A. iwasaki azurin, and Chromatium flavin cytochrome c.